The present invention relates to a method and apparatus for reproducing an encoded video signal, and more particularly, to an improved method and apparatus for reproducing an encoded video signal to produce a smooth video signal.
A variety of electronic devices that support multimedia have been developed in recent years. Such electronic devices include digital video players, set top boxes, digital TVs, digital VCRs, and personal computers. These electronic devices have decoders for reproducing video data that has been encoded using highly efficient coding schemes for videos such as MPEG-2/MPEG-4.
Generally, in these decoders, after a video signal is decoded, a post filter filters the decoded video signal to improve the image quality. Most coding schemes such as MPEG-2/MPEG-4 process video images in blocks, which degrades the decoded image with block noise and edge noise. Block noise is distortion in the decoded signal that appears as block patterns that are not present in the original video image. Edge noise is ringing-like noise (also referred to as “mosquito noise”) that occurs near edges.
The post filter removes such noises inherent in the coding scheme. The post filter smoothes a decoded video signal to remove high frequency components in a boundary region between blocks. A decoding apparatus that has such a post filter is known, for example, from Japanese Patent Publication (KOKAI) No. 64-55987. This document discloses a method of first determining whether a block of a video signal output from a decoder is a dynamic block, which includes movements, or a static block, which does not include movements, and then changing the degree of smoothing in the post filter based on this determination to improve the efficiency of the processing. More specifically, if the block is a static block, then smoothing is not performed or hardly performed on the static block. Conversely, if the block is a dynamic block, then smoothing is performed on the dynamic block.
The above method requires excessive time to perform a relatively large amount of calculations, resulting in a delay in the reproduction of the video signal. For example, in a microprocessor-based system that uses software for decoding, decoding a scene that includes rapid movements uses up the processor resource. This causes frequent reproduction delays. These delays are particularly prominent when a video is decoded and reproduced in software in synchronism with audio, resulting in problems such as discrepancy with the audio and dropped frames.
More specifically, when there is a delay in the reproduction of a video signal, frame skipping is typically performed to compensate for the delay, causing decoding to be omitted for several frames. This results in dropped frames, which makes a reproduced image distorted.
Also, in the above referenced patent publication, smoothing is omitted for static blocks even if the processor is available, resulting in unnecessarily degraded image quality.